A. Summary of the Invention
The present invention provides an apparatus for economically increasing the production capacity of fiber blow spinning units. Additionally, the present invention provides a method and apparatus for collecting blow spun fibers in a single layer batt. Accordingly, the present invention provides a multi-tip linear blow spinning slot die.
B. Background of the Invention
The article, "Superfine Thermoplastic Fibers," by Van A. Wente, Industrial and Engineering Chemistry, Vol. 48, No. 8, August 1956, pp. 1342-46, demonstrates the common methods and devices for blow spinning fibers. The described process includes the steps of heating a spinnable substance to a temperature which will allow it to flow. Following heating, the substance passes, usually under pressure, into a spinning die and through one or more capillaries to form a fiber. Upon exiting the capillary, the fiber is contacted with an attenuating media, usually a gas, which draws or stretches the fiber.
The several types of dies utilized for blow spinning fibers include annular dies and slot dies. Annular and slot dies primarily differ in the manner in which the attenuating gas is directed upon the exiting fiber. In an annular die, the attenuating gas passes parallel to the as-spun fiber. In contrast, slot dies direct the attenuating gas onto the as-spun fiber at an angle determined by the die's cheek plates. While described in terms of a slot die, one skilled in the art will recognize that the present invention has equal application for all types of blow spinning dies.
While the process for blow spinning fibers are well known, efforts continue to maximize the production capacity of the blow spinning die. In general, the production capacity of a die is determined by the flow rate of the spinnable substance through the capillaries, the number/spacing of the capillaries in the die, the length of the die and in general the ability to machine a die of a given length to the necessarily strict tolerances. As recognized by U.S. Pat. No. 3,825,379, the accurate alignment of spinning capillaries over long distances is very difficult. In view of the difficulties in machining long blow spinning dies, the inventors of the current invention sought to develop an alternative means for increasing the production capacity of blow spinning dies.
Accordingly, the present invention provides a multiple tip blow spinning die. The use of a multi-tip die increases the capacity of a single die for any given length. Further, the use of a multi-tip die allows the use of shorter dies without the loss of production capacity. The use of a shorter die is particularly valuable when spinning substances which commonly plug capillaries, such as carbonaceous pitch. When used in production, several shorter dies will take the place of one long die, thereby allowing the operator to service a single die without halting production of an entire line.
Finally, the present invention also provides a process for combining the multiple curtains of fibers generated by the improved spinning apparatus into a single curtain of fibers which may then be collected as a single layer batt on a moving belt. The process combines the improved spinning apparatus with a venturi/diffusion chamber as described in U.S. Pat. No. 5,648,041. In the present invention, the venturi/diffusion chamber has been expanded to provide a single venturi for each curtain of fibers. Subsequently, the curtains pass from each venturi into a single diffusion chamber. Although applicable in almost all blow spinning applications, the process of the present invention is particularly useful when spinning fibers from a carbonaceous pitch such as solvated mesophase pitch.